Lipomatous hemangiopericytoma: A fat-containing variant of solitary fibrous tumor? Clinicopathologic, immunohistochemical, and ultrastructural analysis of a series in favor of a unifying concept

doi:10.1053/hupa.2000.9777

Human Pathology

Volume 31, Issue 9, September 2000, Pages 1108-1115

https://doi.org/10.1053/hupa.2000.9777 Get rights and content

Abstract

The clinicopathologic, immunohistochemical and ultrastructural features of 13 lipomatous hemangiopericytomas are presented. There were 6 male and 7 female patients whose ages at diagnosis ranged from 27 to 75 years (median 48) all presenting with a mass of variable duration. The tumor sizes ranged from 1.7 cm to 19 cm (median 5.5 cm). The locations included the orbit (1), neck (1), mediastinum (1), epicardium (1), retroperitoneum (3), right iliac fossa (1), and upper (1) and lower (4) extremity. Histologically, the lesions were composed of a varying admixture of spindle-shaped to round cells, variably collagenous stroma, adipose tissue, and branched, often thick-walled, hemangiopericytoma-like vessels. For 11 tumors, the mitotic activity ranged from 1 to 3 mitoses per 10 high-power fields (HPF). One tumor which contained hypercellular areas showed 13 mitoses per 10 HPF, and another hypercellular lesion showed up to 43 mitoses per 10 HPF, abnormal mitoses, and necrosis. Immunohistochemically, tumor cells were invariably positive for vimentin and CD99, and mostly for CD34 but negative for desmin, keratin, CD31, CD117 (c-kit), and inhibin. About half of the tumors showed reactivity for bcl-2. Occasionally, focal reactivity was also observed for smooth muscle actin, muscle-specific actin, S100 protein, and epithelial membrane antigen. Ultrastructural examination of seven cases showed features in keeping with fibroblastic, myofibroblastic, or pericytic differentiation. Treatment consisted of simple tumorectomy in 10 cases and wide excision in 3. Follow-up information on 10 patients (range: 6 to 77 months; median: 18 months) showed no recurrence. Lipomatous hemangiopericytoma which share the clinical, pathologic, immunohistochemical, and ultrastructural features of solitary fibrous tumor (SFT) is likely to represent, in most cases, a fat-containing variant of SFT. HUM PATHOL 31:1108-1115.

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We describe a case of fat-forming solitary fibrous tumor (SFT) of the orbit with typical findings on imaging that may improve the awareness of orbital fat-forming SFT.
An 88-year-old female presented with exophthalmos and pain in her right eye. Preoperative imaging showed an oval, well-defined mass with soft-tissue density, interspersed with a well-circumscribed lesion. The lesion showed low-density in computed tomography (CT) scans, hyperintense in T1/T2 weighted images of magnetic resonance imaging (MRI) scans and hypointense in fat-suppressed images of MRI scans. The tumor was removed en bloc and diagnosed as low-grade malignant fat-forming SFT by pathological examination. There was no evidence of recurrence 9-month postoperatively.
The imaging feature of orbital fat-forming SFT is a well-defined solid tumor interspersed with adipose tissue. Such findings are vital for the preoperative diagnosis and the choice of the treatment.
Solitary fibrous tumor: Can the new Huang risk stratification system for orbital tumors improve prognostic accuracy in other tumor locations?
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Solitary fibrous tumors (SFTs) are known for their heterogeneous morphology, characterized by a variety of cell shapes and different growth patterns. They can also arise in various anatomical locations, most commonly in extremities and deep soft tissues. Despite this diversity in morphology and location, all SFTs share a common molecular signature involving the NAB2::STAT6 gene fusion. Due to their unpredictable clinical behavior, establishing prognostic factors is crucial. This study aims to evaluate an orbital risk stratification system (RSS) proposed by Huang et al. for use in extraorbital SFTs using a database of 97 cases. The Huang model takes into consideration tumor size, mitotic figures, Ki-67 index, and dominant constituent cell (DCC) as key variables. Survival analysis confirmed the model's predictive value, with higher-risk scores being associated with poorer outcomes. However, in contrast to the orbital SFTs studied by Huang et al., our study did not find a correlation between tumor size and recurrence in extraorbital cases. While the Huang model performs slightly better than other RSS, it falls short on achieving statistical significance in distinguishing recurrence risk groups in extraorbital locations. In conclusion, this study validates the Huang RSS for use in extraorbital SFTs and underscores the importance of considering DCC, mitotic count, and Ki-67 together. However, we found that including tumor size in this model did not improve prognostic significance in extraorbital SFTs. Despite the benefits of this additional RSS, vigilant monitoring remains essential, even in cases classified as low-risk due to the inherent unpredictability of SFT clinical outcomes.
Toward Better Understanding and Management of Solitary Fibrous Tumor
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Citation Excerpt :
Tumor necrosis is uncommon and must be distinguished from intratumoral hemorrhage. Variants of SFT include lipomatous (fat-forming) SFT14–16 and giant cell-rich SFT, which contains multinucleated, stellate stromal cells that often line pseudovascular spaces in the tissue (Fig. 2C–D).17,18 Anaplastic SFTs have undergone progression to outright sarcoma and usually show areas of recognizable SFTs juxtaposed to a high-grade undifferentiated sarcoma.
Fat-forming solitary fibrous tumor with NAB2/ STAT6 gene fusion. Case report of genial location and literature review
2022, Revista Espanola de Patologia
El tumor fibroso solitario variedad lipomatosa es una neoplasia de partes blandas compuesta por tejido adiposo maduro y áreas de hemangiopericitoma. Un varón de 53 años se presentó clínicamente con asimetría facial. La resonancia magnética maxilofacial demostró una lesión quística, de 3 x 2 cm, por delante de la pared anterior del seno maxilar. Histológicamente, había áreas fusocelulares densas que expresaban CD34, CD99, Bcl-2 y STAT6, zonas mixoides, vasos sanguíneos hemangiopericitomatosos y adipocitos S100 positivos. La fusión génica NAB2/STAT6 fue revelada mediante RT-PCR. El principal diagnóstico diferencial se planteó con el lipoma de células fusiformes y la variante maligna del tumor fibroso solitario lipomatoso. La sobreexpresión de STAT6 y la fusión génica NAB2-STAT6 son específicas del tumor fibroso solitario lipomatoso y la presencia de lipoblastos y áreas de tumor lipomatoso atípico sugiere malignidad. Estos tumores en cabeza y cuello tienen un comportamiento biológico benigno.
The lipomatous variety solitary fibrous tumor is a soft tissue neoplasm composed of mature adipose tissue and hemangiopericytoma areas. A 53-year-old man consulted for facial asymmetry and maxillofacial magnetic resonance imaging showed a cystic lesion, 3 x 2 cm in size, in front of the anterior wall of the maxillary sinus. Histologically, there were dense spindle cells expressing CD34, CD99, Bcl-2, and STAT6, myxoid zones, hemangiopericytomatous blood vessels, and S100 positive adipocytes. NAB2/STAT6 gene fusion was revealed by RT-PCR. The main differential diagnosis was raised with the spindle cell lipoma and malignant variant of the lipomatous solitary fibrous tumor. STAT6 overexpression and NAB2/STAT6 gene fusion are specific for lipomatous solitary fibrous tumor and the presence of lipoblasts and atypical lipomatous tumor areas suggests malignancy. These tumors located in the head and neck region have a benign biological behavior.
Atypical spindle cell/pleomorphic lipomatous tumor of the stomach: A case report
2021, Human Pathology: Case Reports
Citation Excerpt :
The tumor shows hypocellular and hypercellular areas composed of spindle to round cells, prominent branching blood vessels, variable adipocytic component, and collagenous/myxoid stroma. STAT6 is a highly sensitive IHC marker for SFT [11,15–17]. In conclusion, we report the first case of ASPLT in the upper gastrointestinal tract, an extremely uncommon location for the tumor.
Atypical spindle cell/pleomorphic lipomatous tumor (ASPLT) is a newly accepted entity that belongs to the group of low-grade adipocytic neoplasms. ASPLT commonly manifests a soft tissue mass in both upper and lower extremities but is extremely rare in the gastrointestinal tract. Here we report a case of a gastric ASPLT in a 59-year-old male, who presented for the evaluation of new onset of dysphagia. To our best knowledge, this is the first case report of ASPLT in the upper gastrointestinal tract.
Lipomatous Solitary Fibrous Tumors Harbor Rare NAB2-STAT6 Fusion Variants and Show Up-Regulation of the Gene PPARG, Encoding for a Regulator of Adipocyte Differentiation
2021, American Journal of Pathology
Solitary fibrous tumors (SFTs) harbor activating NAB2-STAT6 gene fusions. Different variants of the NAB2-STAT6 gene fusion have been associated with distinct clinicopathologic features. Lipomatous SFTs are a morphologic variant of SFTs, characterized by a fat-forming tumor component. Our aim was to evaluate NAB2-STAT6 fusion variants and to further study the molecular genetic features in a cohort of lipomatous SFTs. A hybrid-capture–based next-generation sequencing panel was employed to detect NAB2-STAT6 gene fusions at the RNA level. In addition, the RNA expression levels of 507 genes were evaluated using this panel, and were compared with a control cohort of nonlipomatous SFTs. Notably, 5 of 11 (45%) of lipomatous SFTs in the current series harbored the uncommon NAB2 exon 4–STAT6 exon 4 gene fusion variant, which is observed in only 0.9% to 1.4% of nonlipomatous SFTs. Furthermore, lipomatous SFTs displayed significant differences in gene expression compared with their nonlipomatous counterparts, including up-regulation of the gene peroxisome proliferator activated receptor-γ (PPARG). Peroxisome proliferator activated receptor-γ is a nuclear receptor regulating adipocyte differentiation, providing a possible explanation for the fat-forming component in lipomatous SFTs. In summary, the current study provides a possible molecular genetic basis for the distinct morphologic features of lipomatous SFTs.

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Original ContributionsLipomatous hemangiopericytoma: A fat-containing variant of solitary fibrous tumor? Clinicopathologic, immunohistochemical, and ultrastructural analysis of a series in favor of a unifying concept

Abstract

Original Contributions
Lipomatous hemangiopericytoma: A fat-containing variant of solitary fibrous tumor? Clinicopathologic, immunohistochemical, and ultrastructural analysis of a series in favor of a unifying concept